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When a magnetically confined plasma is heated strongly, it may spontaneously transition from a low confinement (or L-mode) state to a high confinement (or H-mode) state. | When a magnetically confined plasma is heated strongly, it may spontaneously transition from a low confinement (or L-mode) state to a high confinement (or H-mode) state. | ||
<ref>[http://link.aps.org/doi/10.1103/PhysRevLett.53.1453 F. Wagner et al, ''Development of an Edge Transport Barrier at the H-Mode Transition of ASDEX'', Phys. Rev. Lett. '''53''' (1984) 1453 - 1456]</ref> | <ref>[http://link.aps.org/doi/10.1103/PhysRevLett.53.1453 F. Wagner et al, ''Development of an Edge Transport Barrier at the H-Mode Transition of ASDEX'', Phys. Rev. Lett. '''53''' (1984) 1453 - 1456]</ref> | ||
In the H-mode, the energy confinement time is significantly enhanced, i.e., typically by | In the H-mode, the energy confinement time is significantly enhanced, i.e., typically by a factor of 2 or more. | ||
<ref>[http://dx.doi.org/10.1088/0741-3335/29/10A/320 M. Keilhacker, ''H-mode confinement in tokamaks'', Plasma Phys. Control. Fusion '''29''' (1987) 1401-1413]</ref> | |||
This transport bifurcation is the consequence of the suppression of turbulence in the edge plasma, associated with a | This transport bifurcation is the consequence of the suppression of turbulence in the edge plasma, associated with a sheared flow layer and an associated edge radial electric field. | ||
The precise mechanism governing this phenomenon is the subject of ongoing studies. | The precise mechanism governing this phenomenon is the subject of ongoing studies. | ||
The steep edge gradients lead to quasi-periodic violent relaxation phenomena, known as Edge Localized Modes (ELMs), which have a strong impact on the surrounding vessel. | The transition occurs spontaneously when a certain threshold value of the heating is exceeded. | ||
The steep edge gradients (of density and temperature) lead to quasi-periodic violent relaxation phenomena, known as Edge Localized Modes (ELMs), which have a strong impact on the surrounding vessel. | |||
== References == | == References == | ||
<references /> | <references /> | ||